8‐Oxabicyclo[3.2.1]oct‐6‐en‐3‐one: Anwendungen in der asymmetrischen Synthese polyoxygenierter Bausteine

Abstract

Die Entdeckung und das Design von zuverlässigen und effizienten Methoden zum Aufbau chiraler Bausteine spielt in der modernen Naturstoffsynthese eine entscheidende Rolle. 8‐Oxabicyclo[3.2.1]oct‐6‐en‐3‐one sind leicht zugängliche Gerüste mit definierten stereochemischen Eigenschaften, die in Nicht‐Aldolansätzen zur Herstellung chiraler Bausteine genutzt werden. Strategien zu ihrer enantioselektiven Synthese umfassen Methoden für asymmetrische Cycloadditionen, Desymmetrisierungsprotokolle und “Racemic‐Switch‐Operationen”. Die Ergebnisse dieser Arbeiten werden in diesem Aufsatz präsentiert und eingeschätzt.

Gold‐Catalyzed [4C+3C] Intramolecular Cycloaddition of Allenedienes: Synthetic Potential and Mechanistic Implications

“…The above-mentioned results (Table 1, entries [1][2][3][4][5] clearly indicate that the use of complex A is critical for the success in cycloadditions involving terminally monosubstituted allenes such as 1 b-e. Noteworthy, the well known synthetic potential of oxabridged systems similar to those present in products 7 c-e, bodes well for the potential applicability of the method in the preparation of target-relevant bicarbocyclic systems. [10] As can be seen in Table 1, the presence of substituents at the diene unit was well tolerated (1 f-h, Table 1, entries [6][7][8], and the corresponding [4C + 3C] cycloadducts were obtained in good yields (77-93 %), and with complete stereocontrol. Surprisingly, the reaction of cyclopentylallene derivative 1 i in the presence of catalyst A, in addition to providing the expected tricycle 7 i that results from a 1,2 alkyl shift in the intermediate carbene species, led also to a minor cycloadduct identified as the bicycle 8 i (Table 1, entry 9).…”

Nonaflates from 8‐Oxabicyclo[3.2.1]oct‐6‐en‐3‐ones as Building Blocks for Diversity‐Orientated Synthesis: Preparation, Heck‐Couplings and Subsequent Diels–Alder Reactions

“…[20] Experimental Section General Information NMR spectra were recorded on Bruker WH 270, Bruker AC 500 and Joel Eclipse 500 (500 MHz) instruments. 1 H and 13 C chemical shifts are expressed as ppm downfield from tetramethylsilane (d ¼ 0) used as an internal standard. 13 C NMR signals of CF 3 (CF 2 ) 3 groups are not given since unambiguous assignment is not possible due to strong splitting by coupling with the 19 F nuclei.…”

“…[1,2] The bicyclo[3.2.1]octane core of these molecules is densely functionalized and is accessible with a wide variety of substituents at the C-2 and C-4 positions. Further functionalizations, cleavage of the oxygen bridge, [3,4] or ring annulations [5] at the double bond are possible.…”

The Cycloaddition Strategy for the Synthesis of Natural Products Containing Carbocyclic Seven‐Membered Rings

“…[1] Unlike the other common ring sizes (five and six), seven-membered rings are difficult to access by direct cyclization reactions due to a combination of entropic factors and the development of nonbonded interactions in the transition state. These difficulties can be overcome if a cycloaddition rather than a cyclization approach is followed, whereby two of the bonds in the cyclic framework are formed simultaneously or almost simultaneously.…”